Programmable cells of the above type are widely used in integrated circuits, such as programmable read only memories and programmable logic devices.
The programmable component may comprise, for instance, an electrically programmable fuse or anti-fuse. The component is programmed by modifying its physical or chemical character, for instance, by means of a high current. The heat that is generated by the current in the component causes, for instance, deformation of a conductive signal path through melting or the inclusion or formation of substances that change the path's originally conductive or isolating state.
In the known cell the programmable connection typically consists of a transistor having its control electrode coupled to the cell input and having its main current path placed between a supply voltage terminal and the output in series with the component. Consequently, the component is located in the signal path between the cell input and the output. Examples of such cells are shown in U.S. Pat. No. 4,814,646, FIG. 3c.
Such a series arrangement of the transistor and the programmable component requires the transistor to be quite large in order to provide a sufficiently high current to alter the component during programming of the cell. A bipolar transistor that is connected to the component typically has an emitter area of 2.times.10 um.sup.2, which is quite large. However, accessing the cell, i.e., supplying an input signal and detecting the associated output signal, does not require such a large transistor. In addition to the large area, the attendant large parasitic capacitance is another disadvantage since it limits charging and discharging speeds at the various transistor nodes.